Aging alters the properties of somatic cells, resulting in declines in tissue and organ function. Reprogramming of somatic cells to induced pluripotent stem cells (iPS cells) provides the opportunity to test whether aging at the cell level is reversible and whether the changes in cell properties that are caused by aging can be erased and the cell returned to a completely pluripotent state. A novel aspect of this proposal is that our reprogramming studies will be performed using cells from a small nonhuman primate, the marmoset. Marmosets have the shortest life span of any anthropoid primate;therefore, they can more efficiently be used to compare reprogramming in early- versus late-life donors. In a future development of the work proposed here, reprogrammed/re-differentiated cells can be transplanted back into the same individual animal from which the somatic cells were derived, thus providing a "gold standard" test of the ability of reprogrammed/redifferentiated cells to function normally in an in vivo environment. Specific Aim 1: We hypothesize that aging will impair reprogramming by transcription factors, so that cells derived from older donors will exhibit a greater tendency to be misprogrammed and less ability to be correctly reprogrammed to a true pluripotent state. This will be tested by the retroviral introduction of reprogramming genes (Oct4, Sox2, Klf4, with or without c-Myc) into skin fibroblasts from marmosets of a range of ages, newborn to very old (~13 years). We will examine reprogramming in resultant cell colonies;defects in reprogramming may be observed as an aging-related increase in misprogramming, producing cells that lack pluripotency and which may have acquired malignant properties instead. If this is correct, future work will aim to elucidate those aging processes that interfere with reprogramming. However, we also anticipate that even at very old age some cells will be correctly reprogrammed to a pluripotent state. Specific Aim 2: We hypothesize that cells that have been correctly reprogrammed to pluripotency, even from old donors, will be able to properly redifferentiate along defined lineages when exposed to appropriate in vitro environments. We propose to induce them to differentiate to dopaminergic neurons. Proper differentiation will be assessed by development of neuronal morphology and expression of dopaminergic neuron-specific markers. If defects in redifferentiation or abnormal cell properties emerge as characteristics of iPS cells formed from old donors, further studies will focus on the nature of these aging-related changes that interfere with redifferentiation. These studies provide the necessary basic science that supports future patient-specific cell therapy. In the marmoset model, we can determine whether cells can be derived from skin biopsies, subjected to reprogramming/redifferentiation, and then safely transplanted back into the donor to exert a desired therapeutic effect, including therapies of late-life diseases such as Parkinson's disease. PUBLIC HEALTH RELEVANCE: Project Narrative Aging causes many changes in cells that eventually result in declines in body function, frailty, and increased susceptibility to diseases. The possibility that these cellular aging changes are reversible has been raised by recent studies that show that it is possible to take skin cells from adults and reprogram them to an embryonic stem cell-like state. In this proposal we will test the effects of aging on the ability to reprogram skin cells from marmoset monkeys, in which there is the potential of retransplanting embryonic stem cell-like cells back into the donor animal to test a therapeutic effect.